The known wheel bearing apparatus for a driven wheel shown in FIG. 4 is a representative structural example of the prior art. This wheel bearing apparatus is referred to as a third generation type. It has an inner member 50, an outer member 51, and double row balls 53, 53 rollably contained, via cages 52, between the inner and outer members 50, 51. The inner member 50 has a wheel hub 54 and an inner ring 55 secured onto the wheel hub 54. The wheel hub 54 has, at its one end, an integrally formed wheel mounting flange 56. The flange 56 mounts a wheel of a vehicle (not shown). The wheel hub outer circumference has an inner raceway surface 54a and a cylindrical portion 54b that axially extends from the inner raceway surface. Hub bolts 58 are secured onto the wheel mounting flange 56 equidistantly along its periphery to mount a wheel and a brake rotor 57.
The inner ring 55 is formed with an inner raceway surface on its outer circumference. The inner ring is press-fit onto the cylindrical portion 54b of the wheel hub 54 via a predetermined interference. The inner ring 55 is prevented from being axially slipped off from the wheel hub 54 by a securing nut 59 fastened to the end of the cylindrical portion 54b. Alternatively, a caulked portion (not shown), formed by plastically deforming the end of the cylindrical portion 54b radially outward, prevents the ring from slipping off of the wheel hub 54.
The outer member 51 is integrally formed with a body mounting flange 62 on its outer circumference. The body mounting flange 62 is mounted on a knuckle 60 that forms part of a suspension apparatus of the vehicle. The outer member 51 inner circumference is formed with double row outer raceway surfaces 51a, 51a. Double row balls 53, 53 are rollably contained between the double row outer raceway surfaces 51a, 51a and the inner raceway surfaces 54a, 55a, arranged opposite to the double row outer raceway surfaces 51a, 51a. (Reference Patent Document: Japanese Laid-open Patent Publication No. 81452/2002).
However, in the prior art wheel bearing apparatus, since the inner circumference of the knuckle 60 is opened so that a pilot portion 61 of the outer member 51 can be inserted therein, several problems occur. One such problem is that the rigidity and strength of the knuckle 60 becomes insufficient. Additionally, foreign material such as rain water or dusts directly splash on seals or a sensor (not shown) arranged on the inner side of the bearing. To solve such a problem, it may be appreciated to eliminate the pilot portion 61 of the outer member 51 so that the inner circumference of the knuckle 60 can be closed. Thus, it is believed that centering between the outer member 51 and the knuckle 60 during their assembly would be difficult and errors would be caused during assembly.